It is apparent that, in particular in top-load washing machines and dryers, or in general in any electric household appliance provided with a rotating member adapted to take a predetermined angular position for allowing unloading or loading, or for providing a specific function of the household appliance itself, it is necessary to accurately detect when the drum or rotating member has taken such predetermined angular position, e.g. in order to stop it accurately in this position by direct controlling the motor means of the rotating member.
It is known from FR-B1-2784403 a detecting device for detecting the angular position of a rotating drum of a top-load washing machine or dryer adapted to allow the stopping of the drum with the loading/unloading opening arranged at the upper tilting top of the electric household appliance; such a device consists in a permanent magnet (or electromagnet) carried facing a RID type sensor by means of a horseshoe-shaped structure which is fixed to the frame of the electric household appliance, outside the tank. The empty space between sensor and magnet is occupied by the pulley of the drive shaft of the drum, on which a ferromagnetic material strip is arranged in predetermined angular position.
When the ferromagnetic material strip periodically passes in the space comprised between sensor and magnet, it alters the magnetic field, allowing the sensor to detect such alteration and consequently emitting an electric signal; such a device is therefore capable of indicating the reaching of a predetermined angular position of the drum, in which the ferromagnetic strip is located between the sensor and the magnet, which are thus intended to be arranged, in use, on opposite sides with respect to the ferromagnetic strip. Such a type of sensor is also possibly adapted to detect the rotation speed of the drum, as described in EP-A-1067232.
The described device presents the drawback of being relatively cumbersome and, above all, of emitting a signal the discrimination of which depends on the distance between sensor and magnet, which may in use vary with respect to the design distance either due to assembly errors, or more simply due to machining tolerances, or due to a deformation of the horseshoe-shaped support which overhangingly carries the sensor and, on the opposite sidethereof, the magnet; therefore, the device according to FR-B1-2784403 is not very reliable.
From DE-C2-3306052 it is further known a device which in order to overcome the aforesaid drawback makes use of two Hall effect sensors arranged in different angular positions operatively associated to a rotating magnet. This second solution, while presenting a higher reliability, presents however a much higher cost and complexity, in addition to a larger size.